Energy Metabolism

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Metabolic Sources of Energy:

• Energy is extracted from food via oxidation, resulting in end products: CO2 and H2O.

• Four stages: hydrolysis in GI, degradation using various pathways, citric acid cycle, and oxidative phosphorylation.

• Access ATP stored as fatty acids and glycogen.

Regulation of Fuel Metabolism:

• Fuels are stored and mobilized depending on the environment.

• Different fuels are utilized depending on the environment - due to insulin/glucagon ratio.

Insulin: promotes fuel storage.

• Glucagon, epinephrine, cortisol, GH: promote fuel utilization.

Glucose Level After Meal:

• Glucose levels rise.

• Insulin released.

• Insulin targets liver, muscle, adipose tissue.

• Glucose stored as glycogen - first.

• Excess glucose stored as fatty acids and triglycerides.

• Brain/RBCs insensitive to insulin; they use glucose directly without the intermediation of insulin.

Glucose Level During Fasting:

• Glucagon and epinephrine levels rise during overnight fast.

• They affect skeletal muscle, adipose tissue, and liver.


• Glycogen is converted to glucose and released into blood.

Skeletal muscle:

• Amino acids released.

Adipose tissue:

• Fatty acids released.

Glucose Level During Starvation:

• Glucagon and epinephrine levels very high.

• Rapid lipolysis.

• Ketone synthesis.

• Lipids and ketone levels increased in blood.

• Muscle uses fatty acids as fuel; brain uses ketones as fuel.

Fuel Metabolism:


• Uses glucose and amino acids.

Adipose tissue:

• Uses: glucose and fatty acids.

Skeletal muscle:

• Resting: uses glucose and fatty acids.

• Active: fast-twitch fibers during intense exercise use glucose; fatty acids used during moderate exercise.

Cardiac muscle:

• Uses fatty acids; ketones used during prolonged fasting.

• Failing heart uses glucose.


• Uses glucose.

• Ketones used during fasting.

Additional Readings:

Basic Biochemistry

1. Nucleic Acid Structure and Organization
2. DNA Replication and Repair
3. Transcription and RNA Processing
4. Genetic Code, Mutations, and Translation
5. Genetic Regulation
6. Recombinant DNA
7. Amino Acids, Proteins, Enzymes
8. Hormones
9. Vitamins
10. Energy Metabolism
11. Glycolysis and Pyruvate Dehydrogenase
12. Citric Acid Cycle and Oxidative Phosphorylation
13. Glycogen, Gluconeogenesis, and Hexose Monophosphate Shunt
14. Lipid Synthesis and Storage
15. Lipid Mobilization and Catabolism
16. Amino Acid Metabolism Disorders
17. Purine and Pyrimidine Metabolism
18. Electron Transport
19. Citric Acid Cycle and Glyoxylate Cycle
20. Glycolysis
21. Pyruvate Metabolism
22. Mitochondrial ATP formation
23. Gluconeogenesis
24. Glycogen Metabolism
25. Nitrogen Fixation (Metabolism) reactions, and Heme Metabolism
26. Amino Acid Metabolism
27. What is Medium Chain Acyl-CoA Dehydrogenase Deficiency (MCADD)?

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